System for abating neural stimulation side effects

ABSTRACT

Various system embodiments comprise a neural stimulation delivery system adapted to deliver a neural stimulation signal for use in delivering a neural stimulation therapy, a side effect detector, and a controller. The controller is adapted to control the neural stimulation delivery system, receive a signal indicative of detected side effect, determine whether the detected side effect is attributable to delivered neural stimulation therapy, and automatically titrate the neural stimulation therapy to abate the side effect. In various embodiments, the side effect detector includes a cough detector. In various embodiments, the controller is adapted to independently adjusting at least one stimulation parameter for at least one phase in the biphasic waveform as part of a process to titrate the neural stimulation therapy. Other aspects and embodiments are provided herein.

FIELD

This application relates generally to medical devices and, moreparticularly, to systems, devices and methods for reducing potentialside effects from neural stimulation.

BACKGROUND

Neural stimulation has been proposed as a therapy for a number ofconditions. Examples of neural stimulation therapies include neuralstimulation therapies for respiratory problems such a sleep disorderedbreathing, blood pressure control such as to treat hypertension, cardiacrhythm management, myocardial infarction and ischemia, heart failure,epilepsy, depression, pain, migraines, eating disorders and obesity, andmovement disorders.

Many proposed neural stimulation therapies include stimulation of adiverse nerve, such as the vagus nerve. The vagus nerve innervates anumber of organs. However, stimulation of the vagus nerve can haveunintended consequences. For example, it has been reported thatstimulation of the vagus nerve may cause an altered voice, coughing,pharyngitis, paresthesia, dyspnea, dyspepsia, nausea and laryngismus.

SUMMARY

Various aspects of the present subject matter relate to a system.Various system embodiments comprise a neural stimulation delivery systemadapted to deliver a neural stimulation signal for use in delivering aneural stimulation therapy, a cough detector adapted to receive a signalfrom a cough sensor for use in detecting a cough, and a controller. Thecontroller is adapted to control the neural stimulation delivery system,receive a signal indicative of detected cough from the cough detector,determine whether the detected cough is attributable to delivered neuralstimulation therapy, and automatically titrate the neural stimulationtherapy to abate the cough. Various system embodiments comprise a neuralstimulation delivery system, a side effect detector, and a controller.The neural stimulation delivery system is adapted to deliver a neuralstimulation signal for use delivering a neural stimulation therapy. Theneural stimulation has a biphasic waveform with a first phase and asecond phase. The side effect detector is adapted to receive a signalfor use in detecting a side effect. The controller adapted to controlthe neural stimulation delivery system, receive a signal indicative ofdetected side effect from the side effect detector, determine whetherthe detected side effect is attributable to delivered neural stimulationtherapy, and automatically titrate the neural stimulation therapy toabate the side effect including independently adjusting at least onestimulation parameter for at least one phase in the biphasic waveform.

Various aspects of the present subject matter relate to a method.According to various embodiments of the method, a neural stimulationtherapy is applied. It is determined whether the neural stimulationtherapy causes a cough, and the neural stimulation therapy is titratedto abate the cough caused by the neural stimulation therapy. Accordingto various embodiments of the method, a neural stimulation therapy isapplied using a biphasic neural stimulation waveform. It is determinedwhether the neural stimulation therapy causes a side effect. The neuralstimulation therapy is titrated to abate the side effect caused by theneural stimulation therapy. At least one phase-specific stimulationparameter in the biphasic waveform is adjusted to provide the therapytitration.

This Summary is an overview of some of the teachings of the presentapplication and not intended to be an exclusive or exhaustive treatmentof the present subject matter. Further details about the present subjectmatter are found in the detailed description and appended claims. Otheraspects will be apparent to persons skilled in the art upon reading andunderstanding the following detailed description and viewing thedrawings that form a part thereof, each of which are not to be taken ina limiting sense. The scope of the present invention is defined by theappended claims and their equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an embodiment of a process to abate side effects whenneural stimulation is applied.

FIG. 2 illustrates an embodiment of a process to abate a cough whenneural stimulation therapy is applied.

FIG. 3 illustrates an embodiment of a process to abate side effects whenneural stimulation is applied that includes independently adjusting atleast one stimulation parameter for at least one phase in a biphasicwaveform.

FIG. 4 illustrates a biphasic waveform with some parameters that can beadjusted in the process illustrated in FIG. 3.

FIG. 5 illustrates a neural stimulator device embodiment adapted toabate neural stimulation side effects, according to various embodiments.

FIG. 6 illustrates a neural stimulator device embodiment adapted toadjust a phase specific stimulation parameter of a biphasic neuralstimulation waveform to abate neural stimulation side effects, accordingto various embodiments.

FIG. 7 illustrates an embodiment of a neural stimulator device.

FIG. 8 illustrates an embodiment of a neural stimulation therapytitration/adjustment module.

FIG. 9 illustrates an implantable medical device (IMD) having a neuralstimulation (NS) component and a cardiac rhythm management (CRM)component, according to various embodiments of the present subjectmatter.

FIG. 10 shows a system diagram of an embodiment of amicroprocessor-based implantable device, according to variousembodiments.

FIG. 11 illustrates a system including an implantable medical device(IMD) and an external system or device, according to various embodimentsof the present subject matter.

FIG. 12 illustrates a system including an external device, animplantable neural stimulator (NS) device and an implantable cardiacrhythm management (CRM) device, according to various embodiments of thepresent subject matter.

FIG. 13 illustrates a system embodiment in which an IMD is placedsubcutaneously or submuscularly in a patient's chest with lead(s)positioned to stimulate a vagus nerve.

FIG. 14 illustrates a system embodiment that includes an implantablemedical device (IMD) with satellite electrode(s) positioned to stimulateat least one neural target.

FIG. 15 illustrates an IMD placed subcutaneously or submuscularly in apatient's chest with lead(s) positioned to provide a CRM therapy to aheart, and with lead(s) positioned to stimulate and/or inhibit neuraltraffic at a neural target, such as a vagus nerve, according to variousembodiments.

FIG. 16 illustrates an IMD with lead(s) positioned to provide a CRMtherapy to a heart, and with satellite transducers positioned tostimulate/inhibit a neural target such as a vagus nerve, according tovarious embodiments.

FIG. 17 is a block diagram illustrating an embodiment of an externalsystem.

DETAILED DESCRIPTION

The following detailed description of the present subject matter refersto the accompanying drawings which show, by way of illustration,specific aspects and embodiments in which the present subject matter maybe practiced. These embodiments are described in sufficient detail toenable those skilled in the art to practice the present subject matter.Other embodiments may be utilized and structural, logical, andelectrical changes may be made without departing from the scope of thepresent subject matter. References to “an”, “one”, or “various”embodiments in this disclosure are not necessarily to the sameembodiment, and such references contemplate more than one embodiment.The following detailed description is, therefore, not to be taken in alimiting sense, and the scope is defined only by the appended claims,along with the full scope of legal equivalents to which such claims areentitled.

Embodiments of the present subject matter provide a device that iscapable of sensing and abating adverse side effects by automaticallyadjusting stimulation intensity. As used herein, the term “abating” asused in “abating side effects” includes terminating the sensed sideeffect, reducing the intensity of the sensed side effect, reducing theintensity of potential future side effects, and avoiding or preventingpotential future side effects. For example, the neural stimulationintensity can be reduced below a side-effect threshold while maintainingstimulation at a therapeutic level. As will be evident to one forordinary skill in the art, upon reading and comprehending thisdisclosure, the present subject matter can be implemented with variousneural stimulation therapies. For example, some embodiments of thepresent subject matter provide an implantable vagal nerve stimulator toprovide anti-remodeling therapy in heart failure or post myocardialinfarction (post-MI) patients.

Various embodiments provide an implantable system to stimulate the vagusnerve using, for example, a cuff around the vagus nerve or anintravascular lead placed proximal to the nerve, such as within aninternal jugular vein (IJV). Neural stimulation can be intermittentlyprovided to the target nerve using a cyclical ON/OFF time. The devicesenses for adverse side effects when neural stimulation is applied.Various embodiments sense for the presence of coughing, a common adverseside effect. Coughing can be characterized as a sudden, violent chestmovement, and may be detected with a variety of different sensors, suchas an accelerometer or acoustic sensor. Upon detection of the sideeffect, the intensity of neural stimulation is automatically adjustedbelow the side-effect threshold. The stimulation intensity can beadjusted by adjusting the amplitude, frequency, duty cycle, and/or pulsewidth of the neural stimulation signal (including for a phase of abiphasic waveform). The side-effect threshold may increase over time,and the intensity of the neural stimulation therapy can increase with itwhile remaining below the side-effect threshold.

In a biphasic wave form, the amplitude and pulse width of the secondphase has been shown to modulate side effects at a fixed first phase.Amplitude and pulse width of both phases may be independently titratedto avoid side effects while maintaining stimulation at a therapeuticlevel. Various embodiments deliver neural stimulation with a train ofcharge-balanced biphasic pulses, and adjust the amplitude and pulsewidth of the second phase to avoid side effects while maintaining theamplitude and pulse width of the first phase at a therapeutic level. Thedevice can deliver a charge-balanced waveform, or balanced within aspecified percentage or threshold, to avoid charge build-up that maydamage nerves over time. The device may also contain an independentmaximum limit on neural stimulation intensity.

Physiology

The nervous system can be used to provide therapy for heart failure,hypertension, cardiac remodeling, and physical conditioning therapy.These are briefly discussed below.

Nervous System

The automatic nervous system (ANS) regulates “involuntary” organs, whilethe contraction of voluntary (skeletal) muscles is controlled by somaticmotor nerves. Examples of involuntary organs include respiratory anddigestive organs, and also include blood vessels and the heart. Often,the ANS functions in an involuntary, reflexive manner to regulateglands, to regulate muscles in the skin, eye, stomach, intestines andbladder, and to regulate cardiac muscle and the muscle around bloodvessels, for example.

The ANS includes the sympathetic nervous system and the parasympatheticnervous system. The sympathetic nervous system is affiliated with stressand the “fight or flight response” to emergencies. Among other effects,the “fight or flight response” increases blood pressure and heart rateto increase skeletal muscle blood flow, and decreases digestion toprovide the energy for “fighting or fleeing.” The parasympatheticnervous system is affiliated with relaxation and the “rest and digestresponse” which, among other effects, decreases blood pressure and heartrate, and increases digestion to conserve energy. The ANS maintainsnormal internal function and works with the somatic nervous system.Afferent nerves convey impulses toward a nerve center, and efferentnerves convey impulses away from a nerve center.

The heart rate and force is increased when the sympathetic nervoussystem is stimulated, and is decreased when the sympathetic nervoussystem is inhibited (the parasympathetic nervous system is stimulated).Cardiac rate, contractility, and excitability are known to be modulatedby centrally mediated reflex pathways. Baroreceptors and chemoreceptorsin the heart, great vessels, and lungs, transmit cardiac activitythrough vagal and sympathetic afferent fibers to the central nervoussystem. Activation of sympathetic afferents triggers reflex sympatheticactivation, parasympathetic inhibition, vasoconstriction, andtachycardia. In contrast, parasympathetic activation results inbradycardia, vasodilation, and inhibition of vasopressin release. Amongmany other factors, decreased parasympathetic or vagal tone or increasedsympathetic tone is associated with the genesis of various arrhythmias,including ventricular tachycardia and atrial fibrillation.

Baroreflex is a reflex triggered by stimulation of a baroreceptor. Abaroreceptor includes any sensor of pressure changes, such as sensorynerve endings in the wall of the auricles of the heart, vena cava,aortic arch and carotid sinus, that is sensitive to stretching of thewall resulting from increased pressure from within, and that functionsas the receptor of the central reflex mechanism that tends to reducethat pressure. Clusters of nerve cells can be referred to as autonomicganglia. These nerve cells can also be electrically stimulated to inducea baroreflex, which inhibits the sympathetic nerve activity andstimulates parasympathetic nerve activity. Autonomic ganglia thus formspart of a baroreflex pathway. Afferent nerve trunks, such as the vagus,aortic and carotid nerves, leading from the sensory nerve endings alsoform part of a baroreflex pathway. Stimulating a baroreflex pathwayand/or baroreceptors inhibits sympathetic nerve activity (stimulates theparasympathetic nervous system) and reduces systemic arterial pressureby decreasing peripheral vascular resistance and cardiac contractility.Baroreceptors are naturally stimulated by internal pressure and thestretching of vessel wall (e.g. arterial wall).

Stimulating the sympathetic and parasympathetic nervous systems can haveeffects other than heart rate and blood pressure. For example,stimulating the sympathetic nervous system dilates the pupil, reducessaliva and mucus production, relaxes the bronchial muscle, reduces thesuccessive waves of involuntary contraction (peristalsis) of the stomachand the motility of the stomach, increases the conversion of glycogen toglucose by the liver, decreases urine secretion by the kidneys, andrelaxes the wall and closes the sphincter of the bladder. Stimulatingthe parasympathetic nervous system (inhibiting the sympathetic nervoussystem) constricts the pupil, increases saliva and mucus production,contracts the bronchial muscle, increases secretions and motility in thestomach and large intestine, and increases digestion in the smallintention, increases urine secretion, and contracts the wall and relaxesthe sphincter of the bladder. The functions associated with thesympathetic and parasympathetic nervous systems are many and can becomplexly integrated with each other.

Neural stimulation can be used to stimulate nerve traffic or inhibitnerve traffic. An example of neural stimulation to stimulate nervetraffic is a lower frequency signal (e.g. within a range on the order of20 Hz to 50 Hz). An example of neural stimulation to inhibit nervetraffic is a higher frequency signal (e.g. within a range on the orderof 120 Hz to 150 Hz). Other methods for stimulating and inhibiting nervetraffic have been proposed, including anodal block of nerve traffic.According to various embodiments of the present subject matter,sympathetic neural targets include, but are not limited to, a peronealnerve, a sympathetic column in a spinal cord, and cardiacpost-ganglionic sympathetic neurons. According to various embodiments ofthe present subject matter, parasympathetic neural targets include, butare not limited to, a vagus nerve, a baroreceptor, and a cardiac fatpad.

Heart Failure

Heart failure refers to a clinical syndrome in which cardiac functioncauses a below normal cardiac output that can fall below a leveladequate to meet the metabolic demand of peripheral tissues. Heartfailure may present itself as congestive heart failure (CHF) due to theaccompanying venous and pulmonary congestion. Heart failure can be dueto a variety of etiologies such as ischemic heart disease.

Heart failure patients have reduced autonomic balance, which isassociated with LV dysfunction and increased mortality. Modulation ofthe sympathetic and parasympathetic nervous systems has potentialclinical benefit in preventing remodeling and death in heart failure andpost-MI patients. Direct electrical stimulation can activate thebaroreflex, inducing a reduction of sympathetic nerve activity andreducing blood pressure by decreasing vascular resistance. Sympatheticinhibition and parasympathetic activation have been associated withreduced arrhythmia vulnerability following a myocardial infarction,presumably by increasing collateral perfusion of the acutely ischemicmyocardium and decreasing myocardial damage.

Hypertension

Hypertension is a cause of heart disease and other related cardiacco-morbidities. Hypertension occurs when blood vessels constrict. As aresult, the heart works harder to maintain flow at a higher bloodpressure, which can contribute to heart failure. Hypertension generallyrelates to high blood pressure, such as a transitory or sustainedelevation of systemic arterial blood pressure to a level that is likelyto induce cardiovascular damage or other adverse consequences.Hypertension has been arbitrarily defined as a systolic blood pressureabove 140 mm Hg or a diastolic blood pressure above 90 mm Hg.Consequences of uncontrolled hypertension include, but are not limitedto, retinal vascular disease and stroke, left ventricular hypertrophyand failure, myocardial infarction, dissecting aneurysm, andrenovascular disease.

A large segment of the general population, as well as a large segment ofpatients implanted with pacemakers or defibrillators, suffer fromhypertension. The long term mortality as well as the quality of life canbe improved for this population if blood pressure and hypertension canbe reduced. Many patients who suffer from hypertension do not respond totreatment, such as treatments related to lifestyle changes andhypertension drugs.

Cardiac Remodeling

Following myocardial infarction (MI) or other cause of decreased cardiacoutput, a complex remodeling process of the ventricles occurs thatinvolves structural, biochemical, neurohormonal, and electrophysiologicfactors. Ventricular remodeling is triggered by a physiologicalcompensatory mechanism that acts to increase cardiac output due toso-called backward failure which increases the diastolic fillingpressure of the ventricles and thereby increases the preload (i.e., thedegree to which the ventricles are stretched by the volume of blood inthe ventricles at the end of diastole). An increase in preload causes anincrease in stroke volume during systole, a phenomena known as theFrank-Starling principle. When the ventricles are stretched due to theincreased preload over a period of time, however, the ventricles becomedilated. The enlargement of the ventricular volume causes increasedventricular wall stress at a given systolic pressure. Along with theincreased pressure-volume work done by the ventricle, this acts as astimulus for hypertrophy of the ventricular myocardium. The disadvantageof dilatation is the extra workload imposed on normal, residualmyocardium and the increase in wall tension (Laplace's Law) whichrepresent the stimulus for hypertrophy. If hypertrophy is not adequateto match increased tension, a vicious cycle ensues which causes furtherand progressive dilatation.

As the heart begins to dilate, afferent baroreceptor and cardiopulmonaryreceptor signals are sent to the vasomotor central nervous systemcontrol center, which responds with hormonal secretion and sympatheticdischarge. It is the combination of hemodynamic, sympathetic nervoussystem and hormonal alterations (such as presence or absence ofangiotensin converting enzyme (ACE) activity) that ultimately accountfor the deleterious alterations in cell structure involved inventricular remodeling. The sustained stresses causing hypertrophyinduce apoptosis (i.e., programmed cell death) of cardiac muscle cellsand eventual wall thinning which causes further deterioration in cardiacfunction. Thus, although ventricular dilation and hypertrophy may atfirst be compensatory and increase cardiac output, the processesultimately result in both systolic and diastolic dysfunction. It hasbeen shown that the extent of ventricular remodeling is positivelycorrelated with increased mortality in post-MI and heart failurepatients.

Therapies

The present subject matter relates to systems, devices and methods forproviding neural stimulation, such as vagus nerve stimulation, andfurther relates to terminating, preventing, or diminishing potentialside effects of neural stimulation. Various embodiments provide astand-alone device, either externally or internally, to provide neuralstimulation therapy. The present subject matter can be implemented incardiac applications for neural stimulation or in non-cardiacapplications for neural stimulation where a diverse nerve (such as thevagus nerve) is stimulated. For example, the present subject matter maydeliver anti-remodeling therapy through neural stimulation as part of apost-MI or heart failure therapy. The present subject matter may also beimplemented in non-cardiac applications, such as in therapies to treatepilepsy, depression, pain, obesity, hypertension, sleep disorders, andneuropsychiatric disorders. Various embodiments provide systems ordevices that integrate neural stimulation with one or more othertherapies, such as bradycardia pacing, anti-tachycardia therapy,remodeling therapy, and the like.

Neural Stimulation Therapies

Examples of neural stimulation therapies include neural stimulationtherapies for respiratory problems such a sleep disordered breathing,for blood pressure control such as to treat hypertension, for cardiacrhythm management, for myocardial infarction and ischemia, for heartfailure, for epilepsy, for depression, for pain, for migraines, foreating disorders and obesity, and for movement disorders. Many proposedneural stimulation therapies include stimulation of the vagus nerve.This listing of other neural stimulation therapies is not intended to bean exhaustive listing. Neural stimulation can be provided usingelectrical, acoustic, ultrasound, light, and magnetic therapies.Electrical neural stimulation can be delivered using any of a nervecuff, intravascularly-fed lead, or transcutaneous electrodes.

Neural Stimulation for Ventricular Remodeling

A therapy involves preventing and/or treating ventricular remodeling.Activity of the autonomic nervous system is at least partly responsiblefor the ventricular remodeling which occurs as a consequence of an MI ordue to heart failure. It has been demonstrated that remodeling can beaffected by pharmacological intervention with the use of, for example,ACE inhibitors and beta-blockers. Pharmacological treatment carries withit the risk of side effects, however, and it is also difficult tomodulate the effects of drugs in a precise manner. Embodiments of thepresent subject matter employ electrostimulatory means to modulateautonomic activity, referred to as anti-remodeling therapy or ART. Whendelivered in conjunction with ventricular resynchronization pacing, alsoreferred to as remodeling control therapy (RCT), such modulation ofautonomic activity acts synergistically to reverse or prevent cardiacremodeling.

Hypertension

One neural stimulation therapy involves treating hypertension bystimulating the baroreflex for sustained periods of time sufficient toreduce hypertension. The baroreflex is a reflex that can be triggered bystimulation of a baroreceptor or an afferent nerve trunk. Baroreflexneural targets include any sensor of pressure changes, such as sensorynerve endings in the wall of the auricles of the heart, cardiac fatpads, vena cava, aortic arch and carotid sinus, that is sensitive tostretching of the wall resulting from increased pressure from within,and that functions as the receptor of the central reflex mechanism thattends to reduce that pressure. Examples of afferent nerve trunks thatcan serve as baroreflex neural targets include the vagus, aortic andcarotid nerves. Stimulating baroreceptors inhibits sympathetic nerveactivity (stimulates the parasympathetic nervous system) and reducessystemic arterial pressure by decreasing peripheral vascular resistanceand cardiac contractility. Baroreceptors are naturally stimulated byinternal pressure and the stretching of the arterial wall. Some aspectsof the present subject matter locally stimulate specific nerve endingsin arterial walls rather than stimulate afferent nerve trunks in aneffort to stimulate a desire response (e.g. reduced hypertension) whilereducing the undesired effects of indiscriminate stimulation of thenervous system. For example, some embodiments stimulate baroreceptorsites in the pulmonary artery. Some embodiments of the present subjectmatter involve stimulating either baroreceptor sites or nerve endings inthe aorta, the chambers of the heart, the fat pads of the heart, andsome embodiments of the present subject matter involve stimulating anafferent nerve trunk, such as the vagus, carotid and aortic nerves. Someembodiments stimulate afferent nerve trunks using a cuff electrode, andsome embodiments stimulate afferent nerve trunks using an intravascularlead positioned in a blood vessel proximate to the nerve, such that theelectrical stimulation passes through the vessel wall to stimulate theafferent nerve trunk.

Physical Conditioning Therapy

Neural stimulation (e.g. sympathetic nerve stimulation and/orparasympathetic nerve inhibition) can mimic the effects of physicalconditioning. It is generally accepted that physical activity andfitness improve health and reduce mortality. Studies have indicated thataerobic training improves cardiac autonomic regulation, reduces heartrate and is associated with increased cardiac vagal outflow. A baselinemeasurement of higher parasympathetic activity is associated withimproved aerobic fitness. Exercise training intermittently stresses thesystem and increases the sympathetic activity during the stress.However, when an exercise session ends and the stress is removed, thebody rebounds in a manner that increases baseline parasympatheticactivity and reduces baseline sympathetic activity. Physicalconditioning can be considered to be a repetitive, high-level exercisethat occurs intermittently over time.

Physical conditioning therapy can be applied as therapy for heartfailure. Examples of other physical conditioning therapies includetherapies for patients who are unable to exercise. For example, physicalconditioning using sympathetic stimulation/parasympathetic inhibitionfor a bed-bound, post-surgical patient in a hospital may enable thepatient to maintain strength and endurance until such time that thepatient is able to exercise again. By way of another example, a morbidlyobese patient may be unable to exercise, but may still benefit from thephysical conditioning therapy. Furthermore, patients with injuries suchas joint injuries that prevent them from performing their normalphysical activities may benefit from the physical conditioning therapy.

Myocardial Stimulation Therapies

Various neural stimulation therapies can be integrated with variousmyocardial stimulation therapies. The integration of therapies may havea synergistic effect. Therapies can be synchronized with each other, andsensed data can be shared between the therapies. A myocardialstimulation therapy provides a cardiac therapy using electricalstimulation of the myocardium. Some examples of myocardial stimulationtherapies are provided below.

A pacemaker is a device which paces the heart with timed pacing pulses,most commonly for the treatment of bradycardia where the ventricularrate is too slow. If functioning properly, the pacemaker makes up forthe heart's inability to pace itself at an appropriate rhythm in orderto meet metabolic demand by enforcing a minimum heart rate. Implantabledevices have also been developed that affect the manner and degree towhich the heart chambers contract during a cardiac cycle in order topromote the efficient pumping of blood. The heart pumps more effectivelywhen the chambers contract in a coordinated manner, a result normallyprovided by the specialized conduction pathways in both the atria andthe ventricles that enable the rapid conduction of excitation (i.e.,depolarization) throughout the myocardium. These pathways conductexcitatory impulses from the sino-atrial node to the atrial myocardium,to the atrio-ventricular node, and thence to the ventricular myocardiumto result in a coordinated contraction of both atria and bothventricles. This both synchronizes the contractions of the muscle fibersof each chamber and synchronizes the contraction of each atrium orventricle with the contralateral atrium or ventricle. Without thesynchronization afforded by the normally functioning specializedconduction pathways, the heart's pumping efficiency is greatlydiminished. Pathology of these conduction pathways and otherinter-ventricular or intra-ventricular conduction deficits can be acausative factor in heart failure, which refers to a clinical syndromein which an abnormality of cardiac function causes cardiac output tofall below a level adequate to meet the metabolic demand of peripheraltissues. In order to treat these problems, implantable cardiac deviceshave been developed that provide appropriately timed electricalstimulation to one or more heart chambers in an attempt to improve thecoordination of atrial and/or ventricular contractions, termed cardiacresynchronization therapy (CRT). Ventricular resynchronization is usefulin treating heart failure because, although not directly inotropic,resynchronization can result in a more coordinated contraction of theventricles with improved pumping efficiency and increased cardiacoutput. Currently, a common form of CRT applies stimulation pulses toboth ventricles, either simultaneously or separated by a specifiedbiventricular offset interval, and after a specified atrio-ventriculardelay interval with respect to the detection of an intrinsic atrialcontraction or delivery of an atrial pace.

CRT can be beneficial in reducing the deleterious ventricular remodelingwhich can occur in post-MI and heart failure patients. Presumably, thisoccurs as a result of changes in the distribution of wall stressexperienced by the ventricles during the cardiac pumping cycle when CRTis applied. The degree to which a heart muscle fiber is stretched beforeit contracts is termed the preload, and the maximum tension and velocityof shortening of a muscle fiber increases with increasing preload. Whena myocardial region contracts late relative to other regions, thecontraction of those opposing regions stretches the later contractingregion and increases the preload. The degree of tension or stress on aheart muscle fiber as it contracts is termed the afterload. Becausepressure within the ventricles rises rapidly from a diastolic to asystolic value as blood is pumped out into the aorta and pulmonaryarteries, the part of the ventricle that first contracts due to anexcitatory stimulation pulse does so against a lower afterload than doesa part of the ventricle contracting later. Thus a myocardial regionwhich contracts later than other regions is subjected to both anincreased preload and afterload. This situation is created frequently bythe ventricular conduction delays associated with heart failure andventricular dysfunction due to an MI. The increased wall stress to thelate-activating myocardial regions is most probably the trigger forventricular remodeling. By pacing one or more sites in a ventricle nearthe infarcted region in a manner which may cause a more coordinatedcontraction, CRT provides pre-excitation of myocardial regions whichwould otherwise be activated later during systole and experienceincreased wall stress. The pre-excitation of the remodeled regionrelative to other regions unloads the region from mechanical stress andallows reversal or prevention of remodeling to occur.

Cardioversion, an electrical shock delivered to the heart synchronouslywith the QRS complex, and defibrillation, an electrical shock deliveredwithout synchronization to the QRS complex, can be used to terminatemost tachyarrhythmias. The electric shock terminates the tachyarrhythmiaby simultaneously depolarizing the myocardium and rendering itrefractory. A class of CRM devices known as an implantable cardioverterdefibrillator (ICD) provides this kind of therapy by delivering a shockpulse to the heart when the device detects tachyarrhythmias. Anothertype of electrical therapy for tachycardia is anti-tachycardia pacing(ATP). In ventricular ATP, the ventricles are competitively paced withone or more pacing pulses in an effort to interrupt the reentrantcircuit causing the tachycardia. Modern ICDs typically have ATPcapability, and deliver ATP therapy or a shock pulse when atachyarrhythmia is detected.

Method Embodiments for Reducing or Preventing Neural Stimulation SideEffects

FIG. 1 illustrates an embodiment of a process to abate side effects whenneural stimulation is applied. A neural stimulation therapy is appliedat 101. According to various embodiments, the neural stimulation isturned on and off during a therapy schedule, and includes a train ofpulses when the stimulation is turned on. At 102, it is determinedwhether a side effect attributable to the neural stimulation isdetected. In various embodiments, for example, it is determined whetherthe neural stimulation and side effects occur at or near the same timeto determine that the neural stimulation causes the side effect. If aside effect is not detected, the process returns to 101 to continue toapply the neural stimulation therapy. If a side-effect is detected, theprocess proceeds to 103 where the intensity of the neural stimulationtherapy is titrated to abate (avoid or diminish) the side effect. Someexamples for titrating the neural stimulation therapy intensity areprovided below with respect to FIG. 8.

Neural stimulation affects physiology 104 through a neural network.Therapy inputs 105 can be sensed or derived using physiology sensors,which can provide a feedback signal used to control the applied neuralstimulation therapy. Physiology sensors or other inputs can be used tosense, determine or otherwise derive that a side effect is occurring, asillustrated at 102. For example, an embodiment includes a cough sensoradapted to determine when a cough is attributable to applied neuralstimulation. Other embodiments use patient or doctor input for use indetermining when a patient is experiencing a side effect attributable tothe neural stimulation.

FIG. 2 illustrates an embodiment of a process to abate a cough whenneural stimulation therapy is applied. A neural stimulation therapy isapplied at 201. According to various embodiments, the neural stimulationis turned on and off during a therapy schedule, and includes a train ofpulses when the stimulation is turned on. At 202, it is determinedwhether a cough attributable to the neural stimulation is detected. Invarious embodiments, it is determined whether the neural stimulation andcough occurs simultaneously to determine that the neural stimulationcauses the cough. If a cough is not detected, the process returns to 201to continue to apply the neural stimulation therapy. If a coughattributable to the neural stimulation is detected, the process proceedsto 203 where the intensity of the neural stimulation therapy is titratedto abate (avoid or diminish) the side effect. Examples for titrating theneural stimulation therapy intensity are provided below with respect toFIG. 8.

Neural stimulation affects physiology 204 through a neural network.Therapy inputs 205 can be sensed or derived using physiology sensors,which can provide a feedback signal used to control the applied neuralstimulation therapy. Physiology sensors or other inputs can be used tosense, determine or otherwise derive that a cough is occurring, asillustrated at 202. An example of a cough sensor includes anaccelerometer capable of detecting a chest movement that can becharacterized as a sudden and violent movement indicative of a cough.For example, once a movement exceeds a threshold, it can be determinedthat a cough occurred. Another example of a cough sensor includes anacoustic detector capable of detecting a cough sound. For example, oncea sound exceeds a threshold, it can be determined that a cough occurred.Other criteria can be placed on the movement or sound to identifycoughs. Various embodiments combine an accelerometer and an acousticsensor to sense a cough.

FIG. 3 illustrates an embodiment of a process to abate side effects whenneural stimulation is applied that includes independently adjusting atleast one stimulation parameter for at least one phase in a biphasicwaveform. A neural stimulation therapy is applied at 301. According tovarious embodiments, the neural stimulation is turned on and off duringa therapy schedule, and includes a train of pulses when the stimulationis turned on. At 302, it is determined whether a side effectattributable to the neural stimulation is detected. In variousembodiments, it is determined whether the neural stimulation and sideeffects occurs simultaneously to determine that the neural stimulationcauses the side effect. If a side effect is not detected, the processreturns to 301 to continue to apply the neural stimulation therapy. If aside-effect is detected, the process proceeds to 303 where the intensityof the neural stimulation therapy is titrated to abate (avoid ordiminish) the side effect. Neural stimulation affects physiology 304through a neural network. Therapy inputs 305 can be sensed or derivedusing physiology sensors, which can provide a feedback signal used tocontrol the applied neural stimulation therapy. Physiology sensors orother inputs can be used to sense, determine or otherwise derive that aside effect is occurring. Other embodiments use patient or doctor inputfor use in determining when a patient is experiencing a side effectattributable to the neural stimulation.

In the illustrated embodiment, the applied neural stimulation therapy301 includes a biphasic waveform. The neural stimulation therapy istitrated 303 in the illustrated embodiment by independently adjustingstimulation parameters for at least one phase in the biphasic waveform.An embodiment adjusts an amplitude of at least one of the phases of thebiphasic waveform as part of a process to titrate the neural stimulationtherapy. An embodiment adjusts a pulse width of at least one of thephases of the biphasic waveform as part of the process to titrate theneural stimulation therapy. Various embodiments adjust both theamplitude and pulse width as part of the titration process.

Various embodiments adjust at least one of the phases to balance, withina specified percentage or threshold, the charges at the electrode/tissueinterface. Charge (Q) and current (I) are related as follows:I=Q/second. Thus, larger current and/or longer pulse width times cancause higher charge build up at an electrode or electrodes, and smallercurrent and/or smaller pulse width times can cause smaller charge buildup at an electrode or electrodes.

FIG. 4 illustrates a biphasic waveform with some parameters that can beadjusted in the process illustrated in FIG. 3. Two biphasic pulses areillustrated. Each biphasic pulse includes a first phase (PW1 illustratedas a positive pulse) and a second phase (PW2 illustrated as a negativepulse). In the illustrated waveform, the first and second phases areseparated by a phase delay. Various embodiments use a biphasic waveformwith no phase delay (a phase delay that is zero). Each of the first andsecond phases of the pulse has an amplitude. According to embodiments ofthe present subject matter, stimulation parameters associated with thefirst and second phases can be independently adjusted. Thus, forexample, the second phase can be adjusted while the first phasemaintains the stimulation parameters. For example, the amplitude ormagnitude of the second phase (PW2) can be reduced to avoid or reduce aside effect, and the pulse width can be lengthened to maintain a chargebalance between the two phases.

FIG. 4 can illustrate either a current biphasic pulse waveform or avoltage biphasic pulse waveform. For a current biphasic pulse waveform,the charge is proportional to current (I) times the pulse width (PW), orQ=I*PW. For a given resistive load (R), current (I) and voltage (V) arerelated as V=IR. Thus, for a voltage biphasic pulse waveform, the chargeis also proportional to voltage (V) time pulse width (PW), orQ=(V/R)*PW. Appropriate circuitry can be designed to predict or measurecharge build up associated with each phase of the biphasic pulse, and toappropriately adjust at least one stimulation parameter for at least oneof the phases of the biphasic pulse to maintain a balance (or a nearbalance within a threshold) of each other. For example, the area in eachpulse can be calculated (area=amplitude*pulse width), and thestimulation parameter(s) for at least one phase are appropriatelyadjusted to generally equalize the areas in both phases, where one phasemaintains therapeutic effectiveness of the neural stimulation and theother phase reduces or eliminates side effects.

Device Embodiments

FIG. 5 illustrates a neural stimulator device embodiment adapted toabate neural stimulation side effects, according to various embodiments.The illustrated device 506 can be an implantable device or an externaldevice. The illustrated device includes a neural stimulation deliverysystem 507 adapted to deliver a neural stimulation signal to the neuralstimulation electrode(s) or transducer(s) 508 to deliver the neuralstimulation therapy. Examples of neural stimulation electrodes includenerve cuff electrodes, intravascularly placed electrodes, andtranscutaneous electrodes. Examples of neural stimulation transducersincludes ultrasound, light and magnetic energy transducers. A controller509 receives therapy inputs 510, and appropriately controls the neuralstimulation therapy delivery system 507 using the therapy inputs 510 toprovide the appropriate neural stimulation signal to theelectrode(s)/transducer(s) that results in a desired intensity of neuralstimulation.

The illustrated device also includes side-effect detection inputs 511and a side event detector 512. Examples of side effects capable of beingdetected by the side effect detector 512 include coughing 513,voice-related side effects 514 such as voice alterations or laryngismus,respiratory-related side effects 515 such as dyspnea and apnea,cardiac-related side effects 516 such as bradycardia, tachyarrhythmias,and reduced cardiac output, and patient discomfort 517 such as nausea,inflammation of throat, abnormal sensations, and upset stomach. Variousinputs 511 can be used by the side effect detector 512. For example, animpedance sensor, an accelerometer 518 and/or acoustic sensor 519 can beused to detect coughing. An acoustic sensor 519 can also be used todetect voice-related side effects. Respiratory sensors 520, such asminute ventilation and transthoracic impedance, can be used to detectrespiratory-related side effects. Cardiac-related side effects can bedetected using heart rate sensors 521, arrhythmia detectors 522, bloodpressure sensors 523, and blood flow sensors 524. Patient discomfort canbe determined by inputs from a patient 525 or physician 526. Advancedpatient management systems can be used to enable the patient and/ordoctor to provide the inputs. The inputs can be provided by computers,programmers, cell phones, personal digital assistants, and the like. Forexample, a patient can determine when an intolerable side effect isoccurring, and report the side effect. The patient can call a callcenter using a regular telephone, a mobile phone, or the internet. Thecommunication can be through a repeater, similar to that used inGuidant's Latitude patient management system. In response, the callcenter (e.g. server in call center) can automatically send informationto the device to adjust or titrate the therapy. The call center caninform the patient's physician of the event. In various embodiments, apatient's report of side effect(s) triggers an interrogation of thedevice. The interrogation can be automatically triggered. The results ofthe device interrogation can be used to determine if and how the therapyshould be adjusted and/or titrated to abate the side effect(s) reportedby the patient. A server can automatically adjust and/or titrate thetherapy using the results of the device interrogation. Medical staff canreview the results of the device interrogation, and program the devicethrough the remote server to provide the desired therapy adjustmentsand/or titrations. The server can communicate results of the deviceinterrogation to the patient's physician, who can provide input ordirection for adjusting and/or titrating the therapy. Combinations ofthese or other inputs can be used to determine whether a patient isexperiencing a side effect. The controller 509 receives a side-effectcontrol signal from the side effect detector. The controller uses theside-effect control signal to appropriately control the neuralstimulation therapy delivery system to avoid or reduce side effectsattributed to the neural stimulation. The controller is able todetermine whether the timing of the experienced side effect correspondsto the timing of the neural stimulator, such that it can be deduced thatthe neural stimulation causes the observed side effect.

FIG. 6 illustrates a neural stimulator device embodiment adapted toadjust a phase specific stimulation parameter of a biphasic neuralstimulation waveform to abate neural stimulation side effects, accordingto various embodiments. The illustrated device 606 can be an implantabledevice or an external device. The illustrated device includes a neuralstimulation delivery system 607 adapted to deliver a neural stimulationsignal to the neural stimulation electrode(s) 608. Examples of neuralstimulation electrodes include nerve cuff electrodes, intravascularlyplaced electrodes, and transcutaneous electrodes. A controller 609receives therapy inputs 610, and appropriately controls the neuralstimulation therapy delivery system 607 using the therapy inputs 610 toprovide the appropriate neural stimulation signal to theelectrode(s)/transducer(s) that results in a desired intensity of neuralstimulation. The illustrated device also includes side-effect detectioninputs 611 and a side event detector 612. Various inputs 611 can be usedby the side effect detector 612 to determine when a side effect is beingexperienced. The controller 609 receives a side-effect control signalfrom the side effect detector 612. The controller uses the side-effectcontrol signal to appropriately control the neural stimulation therapydelivery system to avoid or reduce side effects attributed to the neuralstimulation. The controller is able to determine whether the timing ofthe experienced side effect corresponds to the timing of the neuralstimulator, such that it can be deduced that the neural stimulationcauses the observed side effect.

The neural stimulation therapy delivery system included in theillustrated device 606 includes a biphasic waveform generator 627, and aphase-specific stimulation parameter adjustment 628. Thus, for example,the generator includes means for independently adjusting stimulationparameter(s) for at least one phase in the biphasic waveform. Examplesof adjustable stimulation parameters include an amplitude and/or pulsewidth of either phase of the biphasic pulse. The illustrated embodimentalso includes a charge balance monitor 629, which provides an input tothe phase-specific adjustment of the stimulation parameters for thebiphasic waveform generator.

FIG. 7 illustrates an embodiment of a neural stimulator device. Theillustrated device 706 includes a stimulation output circuit 707 adaptedto deliver a neural stimulation signal to the stimulation electrode(s)or transducer(s). A stimulation control circuit 709 receives a feedbacksignal from a feedback detection circuit 729, and appropriately controlsthe stimulation output circuit 707 to send a desired neural stimulationsignal to the electrode or transducer 708 for use in delivering theneural stimulation therapy. The feedback detection circuit receives asignal from a physiologic response data sensor 730, which can includethe appropriate therapy sensors to provide a closed loop for obtaining adesired therapy response and can include the appropriate sensors todetect a side effect. In various embodiments, the response from thephysiologic response data sensor 730 includes a cardiac activity such asheart rate, HRV, HRT, or PR interval. In various embodiments theresponse includes a non-cardiac response such as respiration, bloodpressure or cough. Contextual sensor(s) or input(s) 731 are alsoillustrated connected to the feedback detection circuit 729 to provide amore complete picture of a patient's physiology. The feedback detectioncircuit can provide the neural stimulation feedback signal based on thesensor(s) 730 and the contextual input(s) 731. The contextual input(s)can be used to avoid incomplete data from affecting the neuralstimulation. Examples of contextual inputs include an activity sensor, aposture sensor and a timer. Any one or combination of two or morecontextual inputs can be used by the feedback detection circuit. Forexample, an elevated heart rate may be representative of exercise ratherthan a reason for titrating the neural stimulation therapy. The therapytitration/adjustment module 732 uses the feedback signal (including dataderived from monitored side effects and including data derived from amonitored therapy response) to modulate or titrate the therapy generatedby the stimulation output circuit 707 to provide the desired therapyresponse while reducing or avoiding potential side effects attributableto the neural stimulation.

FIG. 8 illustrates an embodiment of a neural stimulation therapytitration/adjustment module. The figure illustrates various means fortitrating or modulating the intensity of the neural stimulationAccording to various embodiments, titrating the therapy intensity 833includes changing a stimulation feature 834 (e.g. amplitude, pulseduration, frequency, and/or waveform—including, for example, aphase-specific feature in a biphasic pulse), neural target site 835 (viamultiple electrodes), and/or vector 836 (via the same or differentvectors). Various embodiments titrate therapy by changing the electrodesused to provide the electrical therapy. Thus, given N electrodes, thetherapy can change from using a first set of electrodes selected fromthe N electrodes to a second set of electrodes selected from the Nelectrodes. An electrode can be in one set but not the other, or can bein both sets. Some sets only include electrodes that are not in theother set. Various embodiments perform an iterative process where astimulation is changed and the response is monitored. If appropriateafter a designated time course or predetermined event (e.g. the therapyis not avoiding the side effect) the device will precede to the nextstimulation routine 837.

FIG. 9 illustrates an implantable medical device (IMD) 938 having aneural stimulation (NS) component 939 and a cardiac rhythm management(CRM) component 940 according to various embodiments of the presentsubject matter. The illustrated device includes a controller 941 andmemory 942. According to various embodiments, the controller includeshardware, software, or a combination of hardware and software to performthe neural stimulation and CRM functions. For example, the programmedtherapy applications discussed in this disclosure are capable of beingstored as computer-readable instructions embodied in memory and executedby a processor. For example, therapy schedule(s) and programmableparameters can be stored in memory. According to various embodiments,the controller includes a processor to execute instructions embedded inmemory to perform the neural stimulation and CRM functions. Theillustrated neural stimulation therapy 943 can include any neuralstimulation therapy, such a s a therapy for ventricular remodeling.Various embodiments include CRM therapies 944, such as bradycardiapacing, anti-tachycardia therapies such as ATP, defibrillation andcardioversion, and cardiac resynchronization therapy (CRT). Theillustrated device further includes a transceiver 945 and associatedcircuitry for use to communicate with a programmer or another externalor internal device. Various embodiments include a telemetry coil.

The CRM therapy section 940 includes components, under the control ofthe controller, to stimulate a heart and/or sense cardiac signals usingone or more electrodes. The illustrated CRM therapy section includes apulse generator 946 for use to provide an electrical signal through anelectrode to stimulate a heart, and further includes sense circuitry 947to detect and process sensed cardiac signals. An interface 948 isgenerally illustrated for use to communicate between the controller 941and the pulse generator 946 and sense circuitry 947. Three electrodesare illustrated as an example for use to provide CRM therapy. However,the present subject matter is not limited to a particular number ofelectrode sites. Each electrode may include its own pulse generator andsense circuitry. However, the present subject matter is not so limited.The pulse generating and sensing functions can be multiplexed tofunction with multiple electrodes.

The NS therapy section 939 includes components, under the control of thecontroller, to stimulate a neural stimulation target and/or senseparameters associated with nerve activity or surrogates of nerveactivity such as blood pressure and respiration. Three interfaces 949are illustrated for use to provide neural stimulation. However, thepresent subject matter is not limited to a particular number interfaces,or to any particular stimulating or sensing functions. Pulse generators950 are used to provide electrical pulses to transducer or transducersfor use to stimulate a neural stimulation target. According to variousembodiments, the pulse generator includes circuitry to set, and in someembodiments change, the amplitude of the stimulation pulse, the pulsewidth of the stimulation pulse, the frequency of the stimulation pulse,the burst frequency of the pulse, and the morphology of the pulse suchas a square wave, triangle wave, sinusoidal wave, and waves with desiredharmonic components to mimic white noise or other signals. Sensecircuits 951 are used to detect and process signals from a sensor, suchas a sensor of nerve activity, blood pressure, respiration, and thelike. The interfaces 949 are generally illustrated for use tocommunicate between the controller 944 and the pulse generator 950 andsense circuitry 951. Each interface, for example, may be used to controla separate lead. Various embodiments of the NS therapy section onlyincludes a pulse generator to stimulate a neural target. The illustrateddevice further includes a clock/timer 952, which can be used to deliverthe programmed therapy according to a programmed stimulation protocoland/or schedule.

FIG. 10 shows a system diagram of an embodiment of amicroprocessor-based implantable device, according to variousembodiments. The controller of the device is a microprocessor 1053 whichcommunicates with a memory 1054 via a bidirectional data bus. Thecontroller could be implemented by other types of logic circuitry (e.g.,discrete components or programmable logic arrays) using a state machinetype of design. As used herein, the term “circuitry” should be taken torefer to either discrete logic circuitry or to the programming of amicroprocessor. Shown in the figure are three examples of sensing andpacing channels designated “A” through “C” comprising bipolar leads withring electrodes 1055A-C and tip electrodes 1056A-C, sensing amplifiers1057A-C, pulse generators 1058A-C, and channel interfaces 1059A-C. Eachchannel thus includes a pacing channel made up of the pulse generatorconnected to the electrode and a sensing channel made up of the senseamplifier connected to the electrode. The channel interfaces 1059A-Ccommunicate bidirectionally with the microprocessor 1053, and eachinterface may include analog-to-digital converters for digitizingsensing signal inputs from the sensing amplifiers and registers that canbe written to by the microprocessor in order to output pacing pulses,change the pacing pulse amplitude, and adjust the gain and thresholdvalues for the sensing amplifiers. The sensing circuitry of thepacemaker detects a chamber sense, either an atrial sense or ventricularsense, when an electrogram signal (i.e., a voltage sensed by anelectrode representing cardiac electrical activity) generated by aparticular channel exceeds a specified detection threshold. Pacingalgorithms used in particular pacing modes employ such senses to triggeror inhibit pacing. The intrinsic atrial and/or ventricular rates can bemeasured by measuring the time intervals between atrial and ventricularsenses, respectively, and used to detect atrial and ventriculartachyarrhythmias.

The electrodes of each bipolar lead are connected via conductors withinthe lead to a switching network 1060 controlled by the microprocessor.The switching network is used to switch the electrodes to the input of asense amplifier in order to detect intrinsic cardiac activity and to theoutput of a pulse generator in order to deliver a pacing pulse. Theswitching network also enables the device to sense or pace either in abipolar mode using both the ring and tip electrodes of a lead or in aunipolar mode using only one of the electrodes of the lead with thedevice housing (can) 1061 or an electrode on another lead serving as aground electrode. A shock pulse generator 1062 is also interfaced to thecontroller for delivering a defibrillation shock via shock electrodes1063 and 1064 to the atria or ventricles upon detection of a shockabletachyarrhythmia.

Neural stimulation channels, identified as channels D and E, areincorporated into the device for delivering parasympathetic stimulationand/or sympathetic inhibition, where one channel includes a bipolar leadwith a first electrode 1065D and a second electrode 1066D, a pulsegenerator 1067D, and a channel interface 1068D, and the other channelincludes a bipolar lead with a first electrode 1065E and a secondelectrode 1066E, a pulse generator 1067E, and a channel interface 1068E.Other embodiments may use unipolar leads in which case the neuralstimulation pulses are referenced to the can or another electrode. Invarious embodiments, the pulse generator for each channel outputs atrain of neural stimulation pulses which may be varied by the controlleras to amplitude, frequency, duty-cycle, and the like. In thisembodiment, each of the neural stimulation channels uses a lead whichcan be intravascularly disposed near an appropriate neural target. Othertypes of leads and/or electrodes may also be employed. A nerve cuffelectrode may be used in place of an intravascularly disposed electrodeto provide neural stimulation. In some embodiments, the leads of theneural stimulation electrodes are replaced by wireless links.

The figure illustrates a telemetry interface 1069 connected to themicroprocessor, which can be used to communicate with an externaldevice. The illustrated microprocessor 1053 is capable of performingneural stimulation therapy routines and myocardial (CRM) stimulationroutines. Examples of NS therapy routines include a therapies to providephysical conditioning and therapies to treat ventricular remodeling,hypertension, sleep disordered breathing, blood pressure control such asto treat hypertension, cardiac rhythm management, myocardial infarctionand ischemia, heart failure, epilepsy, depression, for pain, migraines,eating disorders and obesity, and movement disorders. The presentsubject matter is not limited to a particular neural stimulationtherapy. Examples of myocardial therapy routines include bradycardiapacing therapies, anti-tachycardia shock therapies such as cardioversionor defibrillation therapies, anti-tachycardia pacing therapies (ATP),and cardiac resynchronization therapies (CRT).

System Embodiments

FIG. 11 illustrates a system 1170 including an implantable medicaldevice (IMD) 1171 and an external system or device 1172, according tovarious embodiments of the present subject matter. Various embodimentsof the IMD include a combination of NS and CRM functions. The IMD mayalso deliver biological agents and pharmaceutical agents. The externalsystem and the IMD are capable of wirelessly communicating data andinstructions. In various embodiments, for example, the external systemand IMD use telemetry coils to wirelessly communicate data andinstructions. Thus, the programmer can be used to adjust the programmedtherapy provided by the IMD, and the IMD can report device data (such asbattery and lead resistance) and therapy data (such as sense andstimulation data) to the programmer using radio telemetry, for example.According to various embodiments, the IMD stimulates/inhibits a neuraltarget to provide a neural stimulation therapy with the capability toavoid or diminish side effects from the neural stimulation. For example,an embodiment delivers vagus nerve stimulation and avoids or diminishescoughs attributable to the neural stimulation.

The external system allows a user such as a physician or other caregiveror a patient to control the operation of the IMD and obtain informationacquired by the IMD. In one embodiment, external system includes aprogrammer communicating with the IMD bi-directionally via a telemetrylink. In another embodiment, the external system is a patient managementsystem including an external device communicating with a remote devicethrough a telecommunication network. The external device is within thevicinity of the IMD and communicates with the IMD bi-directionally via atelemetry link. The remote device allows the user to monitor and treat apatient from a distant location. The patient monitoring system isfurther discussed below.

The telemetry link provides for data transmission from implantablemedical device to external system. This includes, for example,transmitting real-time physiological data acquired by IMD, extractingphysiological data acquired by and stored in IMD, extracting therapyhistory data stored in implantable medical device, and extracting dataindicating an operational status of the IMD (e.g., battery status andlead impedance). Telemetry link also provides for data transmission fromexternal system to IMD. This includes, for example, programming the IMDto acquire physiological data, programming IMD to perform at least oneself-diagnostic test (such as for a device operational status), andprogramming the IMD to deliver at least one therapy.

FIG. 12 illustrates a system 1270 including an external device 1272, animplantable neural stimulator (NS) device 1273 and an implantablecardiac rhythm management (CRM) device 1274, according to variousembodiments of the present subject matter. Various aspects involve amethod for communicating between an NS device and a CRM device or othercardiac stimulator. In various embodiments, this communication allowsone of the devices 1273 or 1274 to deliver more appropriate therapy(i.e. more appropriate NS therapy or CRM therapy) based on data receivedfrom the other device. Some embodiments provide on-demandcommunications. In various embodiments, this communication allows eachof the devices to deliver more appropriate therapy (i.e. moreappropriate NS therapy and CRM therapy) based on data received from theother device. The illustrated NS device and the CRM device are capableof wirelessly communicating with each other, and the external system iscapable of wirelessly communicating with at least one of the NS and theCRM devices. For example, various embodiments use telemetry coils towirelessly communicate data and instructions to each other. In otherembodiments, communication of data and/or energy is by ultrasonic means.Rather than providing wireless communication between the NS and CRMdevices, various embodiments provide a communication cable or wire, suchas an intravenously-fed lead, for use to communicate between the NSdevice and the CRM device. In some embodiments, the external systemfunctions as a communication bridge between the NS and CRM devices.

FIGS. 13-16 illustrate system embodiments adapted to provide vagalstimulation, and are illustrated as bilateral systems that can stimulateboth the left and right vagus nerve. Those of ordinary skill in the artwill understand, upon reading and comprehending this disclosure, thatsystems can be designed to stimulate only the right vagus nerve, systemscan be designed to stimulate only the left vagus nerve, and systems canbe designed to bilaterally stimulate both the right and left vagusnerves.

FIG. 13 illustrates a system embodiment in which an IMD 1375 is placedsubcutaneously or submuscularly in a patient's chest with lead(s) 1376positioned to stimulate a vagus nerve. According to various embodiments,neural stimulation lead(s) 1376 are subcutaneously tunneled to a neuraltarget, and can have a nerve cuff electrode to stimulate the neuraltarget. Some vagus nerve stimulation lead embodiments areintravascularly fed into a vessel proximate to the neural target, anduse electrode(s) within the vessel to transvascularly stimulate theneural target. For example, some embodiments stimulate the vagus usingelectrode(s) positioned within the internal jugular vein. Otherembodiments deliver neural stimulation to the neural target from withinthe trachea, the laryngeal branches of the internal jugular vein, andthe subclavian vein. The neural targets can be stimulated using otherenergy waveforms, such as ultrasound and light energy waveforms. Otherneural targets can be stimulated, such as cardiac nerves and cardiac fatpads. The illustrated system includes leadless ECG electrodes on thehousing of the device. These ECG electrodes 1377 are capable of beingused to detect heart rate, for example.

FIG. 14 illustrates a system embodiment that includes an implantablemedical device (IMD) 1475 with satellite electrode(s) 1478 positioned tostimulate at least one neural target. The satellite electrode(s) areconnected to the IMD, which functions as the planet for the satellites,via a wireless link. Stimulation and communication can be performedthrough the wireless link. Examples of wireless links include RF linksand ultrasound links. Examples of satellite electrodes includesubcutaneous electrodes, nerve cuff electrodes and intravascularelectrodes. Various embodiments include satellite neural stimulationtransducers used to generate neural stimulation waveforms such asultrasound and light waveforms. The illustrated system includes leadlessECG electrodes on the housing of the device. These ECG electrodes 1477are capable of being used to detect heart rate, for example.

FIG. 15 illustrates an IMD 1575 placed subcutaneously or submuscularlyin a patient's chest with lead(s) 1579 positioned to provide a CRMtherapy to a heart, and with lead(s) 1576 positioned to stimulate and/orinhibit neural traffic at a neural target, such as a vagus nerve,according to various embodiments. According to various embodiments,neural stimulation lead(s) are subcutaneously tunneled to a neuraltarget, and can have a nerve cuff electrode to stimulate the neuraltarget. Some lead embodiments are intravascularly fed into a vesselproximate to the neural target, and use transducer(s) within the vesselto transvascularly stimulate the neural target. For example, someembodiments target the vagus nerve using electrode(s) positioned withinthe internal jugular vein.

FIG. 16 illustrates an IMD 1675 with lead(s) 1679 positioned to providea CRM therapy to a heart, and with satellite transducers 1678 positionedto stimulate/inhibit a neural target such as a vagus nerve, according tovarious embodiments. The satellite transducers are connected to the IMD,which functions as the planet for the satellites, via a wireless link.Stimulation and communication can be performed through the wirelesslink. Examples of wireless links include RF links and ultrasound links.Although not illustrated, some embodiments perform myocardialstimulation using wireless links. Examples of satellite transducersinclude subcutaneous electrodes, nerve cuff electrodes and intravascularelectrodes.

FIG. 17 is a block diagram illustrating an embodiment of an externalsystem 1780. The external system includes a programmer, in someembodiments. In the illustrated embodiment, the external system includesa patient management system. As illustrated, the external system 1780 isa patient management system including an external device 1781, atelecommunication network 1782, and a remote device 1783. The externaldevice 1781 is placed within the vicinity of an implantable medicaldevice (IMD) and includes an external telemetry system 1784 tocommunicate with the IMD. The remote device(s) 1783 is in one or moreremote locations and communicates with the external device 1781 throughthe network 1782, thus allowing a physician or other caregiver tomonitor and treat a patient from a distant location and/or allowingaccess to various treatment resources from the one or more remotelocations. The illustrated remote device 1783 includes a user interface1785. According to various embodiments, the external device 1781includes a neural stimulator, a programmer or other device such as acomputer, a personal data assistant or phone. The external device 1781,in various embodiments, includes two devices adapted to communicate witheach other over an appropriate communication channel, such as a computerby way of example and not limitation. The external device can be used bythe patient or physician to provide side effect feedback indicative ofpatient discomfort, for example.

One of ordinary skill in the art will understand that the modules andother circuitry shown and described herein can be implemented usingsoftware, hardware, and combinations of software and hardware. As such,the term module is intended to encompass software implementations,hardware implementations, and software and hardware implementations.

The methods illustrated in this disclosure are not intended to beexclusive of other methods within the scope of the present subjectmatter. Those of ordinary skill in the art will understand, upon readingand comprehending this disclosure, other methods within the scope of thepresent subject matter. The above-identified embodiments, and portionsof the illustrated embodiments, are not necessarily mutually exclusive.These embodiments, or portions thereof, can be combined. In variousembodiments, the methods provided above are implemented as a computerdata signal embodied in a carrier wave or propagated signal, thatrepresents a sequence of instructions which, when executed by aprocessor cause the processor to perform the respective method. Invarious embodiments, methods provided above are implemented as a set ofinstructions contained on a computer-accessible medium capable ofdirecting a processor to perform the respective method. In variousembodiments, the medium is a magnetic medium, an electronic medium, oran optical medium.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat any arrangement which is calculated to achieve the same purpose maybe substituted for the specific embodiment shown. This application isintended to cover adaptations or variations of the present subjectmatter. It is to be understood that the above description is intended tobe illustrative, and not restrictive. Combinations of the aboveembodiments as well as combinations of portions of the above embodimentsin other embodiments will be apparent to those of skill in the art uponreviewing the above description. The scope of the present subject mattershould be determined with reference to the appended claims, along withthe full scope of equivalents to which such claims are entitled.

1. A system, comprising: a neural stimulation delivery system configuredto deliver a neural stimulation signal for use in delivering a neuralstimulation therapy; a cough sensor configured to sense a parameter toprovide a signal for use in detecting a cough; a cough detectorconfigured to receive the signal from the cough sensor, to characterizethe signal as a detected cough, and to provide a detected cough signal;a controller configured to control the neural stimulation deliverysystem, receive the detected cough signal from the cough detector,determine whether the detected cough is attributable to delivered neuralstimulation therapy, and automatically titrate the neural stimulationtherapy to abate the cough.
 2. The system of claim 1, wherein the coughdetector includes an accelerometer.
 3. The system of claim 1, whereinthe cough detector includes an acoustic sensor.
 4. The system of claim1, wherein the cough detector includes an impedance sensor.
 5. Thesystem of claim 1, wherein the controller is adapted to automaticallytitrate the neural stimulation therapy to prevent future coughsattributable to the neural stimulation therapy.
 6. The system of claim1, wherein the controller is adapted to automatically titrate the neuralstimulation therapy to diminish future coughs attributable to the neuralstimulation therapy.
 7. The system of claim 1, wherein the neuralstimulation signal includes a biphasic waveform, and the controller isadapted to independently adjust at least one stimulation parameter forat least one phase in the biphasic waveform.
 8. The system of claim 7,further comprising a charge balance monitor adapted to monitor a chargebalance at at least two neural stimulation electrodes and to adjust theat least one stimulation parameter for the at least one phase in thebiphasic waveform to maintain a charge balance to acceptable levels. 9.The system of claim 7, wherein the at least one stimulation parameterincludes an amplitude.
 10. The system of claim 7, wherein the at leastone stimulation parameter includes a pulse width.
 11. The system ofclaim 7, wherein the neural stimulation signal includes a biphasicwaveform with a positive phase and a negative phase, and the controlleris adapted to independently adjust at least one stimulation parameterfor the negative phase in the waveform to avoid future coughsattributable to the neural stimulation therapy.
 12. The system of claim7, wherein the neural stimulation signal includes a biphasic waveformwith a first phase and a second phase, and the controller is adapted toindependently adjust at least one stimulation parameter for the secondphase in the waveform to avoid future coughs attributable to the neuralstimulation therapy and maintain the stimulation parameters for thefirst phase to continue to deliver the neural stimulation therapy.
 13. Asystem, comprising: a neural stimulation delivery system configured todeliver a neural stimulation signal for use in delivering a neuralstimulation therapy, the neural stimulation signal having a biphasicwaveform with a first phase and a second phase; a sensor configured tosense a parameter to provide a signal for use in detecting a sideeffect; a side effect detector configured to receive the signal from thesensor, to characterize the signal as a detected side effect, and toprovide a detected side effect signal; a controller configured tocontrol the neural stimulation delivery system to deliver a therapeuticlevel of the neural stimulation therapy, receive a signal indicative ofthe detected side effect from the side effect detector, determinewhether the detected side effect is attributable to the delivered neuralstimulation therapy, and automatically titrate the neural stimulationtherapy to abate the side effect, wherein in automatically titrating theneural stimulation therapy to abate the side effect, the controller isconfigured to adjust at least one phase-specific stimulation parameterin the biphasic waveform to abate the side effect while maintaining thetherapeutic level of the neural stimulation therapy.
 14. The system ofclaim 13, wherein the detected side effect includes a cough.
 15. Thesystem of claim 13, wherein the detected side effect includes avoice-related side effect.
 16. The system of claim 13, wherein thedetected side effect includes a respiratory-related side effect.
 17. Thesystem of claim 13, wherein the detected side effect includes acardiac-related side effect.
 18. The system of claim 13, wherein thedetected side effect includes patient discomfort.
 19. The system ofclaim 13, further comprising a charge balance monitor adapted to monitora charge balance at at least two neural stimulation electrodes and toadjust the at least one stimulation parameter to maintain a chargebalance within a specified threshold.
 20. A system, comprising: meansfor applying a neural stimulation therapy; means for determining whetherthe neural stimulation therapy causes a cough; and means for titratingthe neural stimulation therapy to abate the cough caused by the neuralstimulation therapy.
 21. The system of claim 20, wherein the means fordetermining whether the neural stimulation therapy causes a coughincludes: means for sensing a physiological parameter using anaccelerometer, an acoustic sensor or an impedance sensor; and means forcharacterizing the sensed physiological parameter as a detected cough.22. A system, comprising: means for applying a neural stimulationtherapy using a biphasic neural stimulation waveform; means fordetermining whether the neural stimulation therapy causes a side effect;and means for titrating the neural stimulation therapy to abate the sideeffect caused by the neural stimulation therapy, wherein the means fortitrating the neural stimulation therapy to abate the side effectincludes means for adjusting at least one phase-specific stimulationparameter in the biphasic waveform to abate the side effect.
 23. Thesystem of claim 22, wherein the means for determining whether the neuralstimulation therapy causes a side effect includes means for determiningwhether the neural stimulation therapy causes a cough, a voice-relatedside effect, a respiratory-related side effect, a cardiac-related sideeffect, or patient discomfort.
 24. A method, comprising: applying aneural stimulation therapy; determining whether the neural stimulationtherapy causes a cough; and titrating the neural stimulation therapy toabate the cough caused by the neural stimulation therapy.
 25. The methodof claim 24, wherein applying a neural stimulation therapy includesapplying a biphasic pulse, and titrating the neural stimulation therapyincludes adjusting at least one phase-specific stimulation parameter inthe biphasic waveform.
 26. The method of claim 24, wherein titrating theneural stimulation therapy to abate the cough caused by the neuralstimulation therapy includes titrating the neural stimulation therapy todiminish the cough caused by the neural stimulation therapy.
 27. Themethod of claim 24, wherein titrating the neural stimulation therapy toabate the cough caused by the neural stimulation therapy includestitrating the neural stimulation therapy to prevent the cough caused bythe neural stimulation therapy.
 28. The method of claim 24, whereindetermining whether the neural stimulation therapy causes a coughincludes detecting a cough and determining whether the detected cough issynchronized to neural stimulation.
 29. The method of claim 24, whereindetermining whether the neural stimulation therapy causes a coughincludes using an acoustic sensor to sense a physiological parameter andcharacterizing the sensed physiological parameter as a detected cough.30. The method of claim 24, wherein determining whether the neuralstimulation therapy causes a cough includes using an accelerometer tosense a physiological parameter and characterizing the sensedphysiological parameter as a detected cough.
 31. The method of claim 24,wherein determining whether the neural stimulation therapy causes acough includes using an impedance sensor to sense a physiologicalparameter and characterizing the sensed physiological parameter as adetected cough.
 32. The method of claim 24, wherein determining whetherthe neural stimulation therapy causes a cough includes determiningwhether the cough occurs concurrently with neural stimulation.
 33. Amethod, comprising: applying a neural stimulation therapy using abiphasic neural stimulation waveform; determining whether the neuralstimulation therapy causes a side effect; and titrating the neuralstimulation therapy to abate the side effect caused by the neuralstimulation therapy, wherein titrating the neural stimulation therapy toabate the side effect includes adjusting at least one phase-specificstimulation parameter in the biphasic waveform to abate the side effect.34. The method of claim 33, further comprising maintaining a chargebuildup at electrode/tissue interfaces to within an acceptablethreshold.
 35. The method of claim 33, wherein determining whether theneural stimulation therapy causes a side effect includes determiningwhether the neural stimulation therapy causes a cough.
 36. The method ofclaim 33, wherein determining whether the neural stimulation therapycauses a side effect includes determining whether the neural stimulationtherapy causes a voice-related side effect.
 37. The method of claim 33,wherein determining whether the neural stimulation therapy causes a sideeffect includes determining whether the neural stimulation therapycauses a respiratory-related side effect.
 38. The method of claim 33,wherein determining whether the neural stimulation therapy causes a sideeffect includes determining whether the neural stimulation therapycauses a cardiac-related side effect.
 39. The method of claim 33,wherein determining whether the neural stimulation therapy causes a sideeffect includes determining whether the neural stimulation therapycauses patient discomfort.
 40. The method of claim 33, whereindetermining whether the neural stimulation therapy causes a side effectincludes determining whether the side effect occurs concurrently withneural stimulation.
 41. The method of claim 33, wherein titrating theneural stimulation therapy to abate the side effect caused by the neuralstimulation therapy includes titrating the neural stimulation to avoidthe side effect.
 42. The method of claim 33, wherein titrating theneural stimulation therapy to abate the side effect caused by the neuralstimulation therapy includes titrating the neural stimulation todiminish the side effect.